BMW E31 840i and 840Ci Alternator Alternate Vendors

If you like, you can skip directly to where you can buy this part.

We sell good, original BMW, used Bosch alternator units. The price is $90 plus shipping.

Assuming I’m reading the parts lists the right way, then the official BMW price for the Bosch part is just over $620 plus a core charge of $50.

Various vendors offer the Bosch part. Pelican Parts is my personal favorite. On general principles, I like buying new parts from them. They offer a rebuilt part for just over $250, plus a core charge of $75.

We don’t charge a core charge. Some of the other vendors I’ve researched do add on a core charge. To redeem that, you have to take or send your old part back to where you did the transaction, within a particular span of dates. This seems reasonable — yet often, this ends up being non-viable in practical reality. In such cases, the core charge ends up as simply one more cost.

We could find a remanufactured unit on eBay too, for slightly more than what we are pricing ours at, but there’s a lot of complexity to buying remanufactured units.

No doubt I can also find many made-in-China units, or rebuilt-somewhere unit, but it becomes pretty subtle when one figures out that many of such units do not include the pulley. That means I would have to somehow get the pulley off the old alternator (which isn’t easy, and would probably require a bench vise, which I don’t own) and then putting it on the replacement alternator (which isn’t easy, and would again require a bench vise). It would also require a torque wrench and the specs to which to torque the attaching nut. Many years ago, I attached such a nut too loosely, it came flying off, and the results were not happy. So when I hear “pulley not included” that’s not good news.

I also found a vendor (whom I didn’t recognize) on Amazon, who offers the Bosch part (new or rebuilt, I’m not sure) for just under $170.

It’s probably safe to say that our used units are price-competitive.

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BMW E31 840i and 840Ci Alternator For Sale, Original Quality, Used, Guaranteed Good Condition

We sell good, original BMW, used alternator units for the BMW E31 8-series.

This part fits the E31 8-Series BMW 840i and 840Ci  made in the following years: 1992, 1993, 1994, 1995, 1996, 1997, 1998 and 1999.

The price is $90.00 plus shipping.

At the time of this writing (Spring 2013) we have no units in stock. We tend to replenish them so I expect we’ll have this item in our inventory indefinitely.

The Bosch part number is AL0742X. This is for the 140A unit. We try to be competitive with affordable prices, friendly service — and you get an original BMW quality part, albeit used.

We sometimes know the car off which the part came, and if the car ran fine, we like to convey that on a case by case basis. For a 20-year old used alternator, please don’t expect a full life-time of service. Here are more details about our satisfaction guarantee.

Please contact our friendly staff, to order your alternator.

BMW E31 8-Series (without the EH transmission) Throttle Position Sensor Typical Problems

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Perhaps the best advice as to removing the throttle position sensor is to not do so prematurely. With the unit in place, and the engine off, remove the plug attached to it, then measure the continuity between the center pin, and the two on either side. Next, ask an assistant to press down slightly on the accelerator pedal while you again measure the continuity. Finally, ask an assistant to press down on the accelerator pedal all the way, while you again measure the continuity. On some cars, the accelerator pedal and cable might be in bad shape, and it might make more sense to yank on the engine side of the accelerator cable, to simulate what your assistant might do.

If the throttle position sensor readings are different with the throttle closed vs. part-way open vs. all the way open, then the throttle position sensor is basically doing what it’s supposed to do.

A more crude yet logical-seeming check that I’ve read about is to unplug the connector at the throttle position sensor, while the engine is running. If the sound of the engine changes, it means the throttle position sensor was having an effect, which means it is basically functional as to the throttle-closed part of its function.

Although the throttle position sensor is important, my impression is that it won’t make a difference as to the engine totally failing to start or run.

The throttle cable end that is attached atop the motor rotates a shaft. Its position is sensed by the throttle position sensor. Following this logic should make it easier to locate the throttle position sensor.

The throttle position sensor attaches with two fasteners, typically screws. Its position is critical. When re-installing it, it’s a good idea to make sure that it senses when the throttle is fully closed and also when it is fully open. The resistance between the outgoing connectors can be measured, and it should change dramatically when the throttle moves to either of those two positions. With the engine not running, you should also be able to hear a slight “click” when the sensor reaches either of those two positions.

As a guideline for the new part, it might be wise to be aware of the position of the part being replaced, before it is removed.

BMW E31 8-Series (without the EH transmission) Throttle Position Sensor Alternate Vendors

If you like, you can skip directly to where you can buy this part.

We sell good, original BMW, used Bosch throttle position sensor units. The price is $30 plus shipping.

Assuming I’m reading the parts lists the right way, then the official BMW price for the Bosch part is just over $90.

Various vendors offer the Bosch part. Pelican Parts is my personal favorite. On general principles, I like buying new parts from them. They offer a new non-Bosch part at a price of just over $45. They also offer new Bosch part at a price of just over $90.

It’s probably safe to say that our used units are price-competitive.

BMW E31 8-Series (without the EH transmission) Throttle Position Sensor Design Difference

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Before the arrival of the ZF 4 HP-22 EH automatic transmission, the kick-down feature of automatic transmissions on the E31 tended to be implemented mechanically.

The EH transmission changed this. The position of the throttle was already being sensed by a throttle position sensor. On models with the EH transmission the throttle position sensor was improved to convey the position of the throttle precisely enough, so that the EH transmission electronics could identify when the driver was requesting a kick-down.

Before this, the throttle position sensor focused on identifying only the throttle-closed position and the wide-open-throttle position. Due to its simplicity, the throttle position sensor for models without the EH transmission has a rectangular 3-wire plug.

By contrast, the throttle position sensor for models with the EH transmission has a round 6-wire plug.

BMW E31 8-Series (without the EH transmission) Throttle Position Sensor Informal Technical Story

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As I understand Bosch fuel injection, the system elicits inputs about the outside world, does math and then sends out instructions to the various components within its control.

One of the inputs of interest is whether or not the driver’s foot is on or off the throttle. These two modes clearly signify a different intent. For that reason, one basic function of the throttle position sensor is to sense which one of the two modes applies.

Another input of interest is whether or not the driver’s foot is pressing the accelerator pedal all the way down. These two modes also signify a very different intent. For that reason, another basic function of the throttle position sensor is to sense which one of the two modes applies.

I own an old BMW 745i and it behaves very differently when the accelerator pedal is all the way down vs. not. Presumably back in 1984 when the car was working correctly, it went way faster with the accelerator pedal all the way down. Nowadays, it stalls. The difference is like night vs. day. I’m guessing that as soon as the throttle position sensor senses that the car is at wide open throttle, it sends a signal to the fuel injection computer, which goes into a special mode, which malfunctions.

As I recall, at wide open throttle, some of the emissions limits are lower, so the fuel injection computer optimizes for maximum power with less of a focus on fuel economy or emissions.

Hypothetically, it might also be of interest to the fuel injection computer at which position the throttle is, even if not fully open or fully closed. However, with the possible mechanical variances in throttle position, I can see how this might be subject to some imprecision, which is probably why the system relies instead on actually measuring how much air is flowing into the intake system.

From what I’ve read, some BMWs do have a rheostat built into the throttle position sensor, but the E31 without the ZF 4 HP-22 EH automatic transmission doesn’t. So, the functions of this part are in some ways a lot more simple:

  • Throttle completely closed, or not
  • Throttle completely open, or not

BMW E31 8-Series (without the EH transmission) Throttle Sensor Removal and Re-Installation

If you like, you can skip directly to where you can buy this part.

Perhaps the best advice as to removing the throttle position sensor is to not do so prematurely. With the unit in place, and the engine off, remove the plug attached to it, then measure the continuity between the center pin, and the two on either side. Next, ask an assistant to press down slightly on the accelerator pedal while you again measure the continuity. Finally, ask an assistant to press down on the accelerator pedal all the way, while you again measure the continuity. On some cars, the accelerator pedal and cable might be in bad shape, and it might make more sense to yank on the engine side of the accelerator cable, to simulate what your assistant might do.

If the throttle position sensor readings are different with the throttle closed vs. part-way open vs. all the way open, then the throttle position sensor is basically doing what it’s supposed to do.

A more crude yet logical-seeming check that I’ve read about is to unplug the connector at the throttle position sensor, while the engine is running. If the sound of the engine changes, it means the throttle position sensor was having an effect, which means it is basically functional as to the throttle-closed part of its function.

Although the throttle position sensor is important, my impression is that it won’t make a difference as to the engine totally failing to start or run.

The throttle cable end that is attached atop the motor rotates a shaft. Its position is sensed by the throttle position sensor. Following this logic should make it easier to locate the throttle position sensor.

The throttle position sensor attaches with two fasteners, typically screws. Its position is critical. When re-installing it, it’s a good idea to make sure that it senses when the throttle is fully closed and also when it is fully open. The resistance between the outgoing connectors can be measured, and it should change dramatically when the throttle moves to either of those two positions. With the engine not running, you should also be able to hear a slight “click” when the sensor reaches either of those two positions.

As a guideline for the new part, it might be wise to be aware of the position of the part being replaced, before it is removed.